Add c_hash to id_token

[HEllRZA]

This PR adds support for c_hash on the id_token.
The c_hash is required in the hybrid flow, and optional otherwise.

According to https://openid.net/specs/openid-connect-core-1_0.html#CodeValidation

If the ID Token is issued from the Authorization Endpoint with a code, which is the case for the response_type values code id_token and code id_token token, this is REQUIRED; otherwise, its inclusion is OPTIONAL.

OpenID Connect Certification
The test (OP-IDToken-c_hash) now succeeds